There are important differences between halo molecules associated with magnetic Feshbach resonances and the naturally occurring halo molecule in \(^{86}\) Sr. With magnetic Feshbach resonances, the relevant scattering and bound molecular states lie on different molecular potentials, and single-photon magnetic-dipole transitions can be used to measure molecular binding energies with RF or microwave spectroscopy [1]}, [2]}, [3]}. Typically, this is done by first forming molecules through magneto-association and then driving bound-free or bound-bound transitions converting the halo molecule into a different state. Other methods include spectroscopy with an oscillating magnetic field [3]}, a modulated optically controlled Feshbach resonance [5]}, and Ramsey-type measurements of atom-molecule oscillation frequencies [6]}. It is also possible to efficiently populate halo states with a magnetic-field sweep [7]} or evaporative cooling [8]} near a magnetic Feshbach resonance [1]}. These are powerful techniques for manipulating quantum gases of alkali metals and other open-shell atoms, for which there are many magnetic Feshbach resonances. Strontium, however, due to its closed-shell electronic structure, lacks magnetic Feshbach resonances in the electronic ground state.
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